Sparking plug connector for an internal combustion engine

ABSTRACT

The invention relates to a spark plug connector for an internal combustion engine, comprising 
     a plug-in contact (28) for the electrode connection of a spark plug; 
     a connector sleeve (3) surrounding the plug-in contact (28); 
     a connection (32) for an ignition cable; 
     a single-piece, rigid, supporting connector sleeve (3) made of an insulating material; and 
     an elastic means (20) attached to the connector sleeve (3) which seals the gap (22) between the connector sleeve and a spark plug well of an engine cylinder, with the spark plug connector being guided in the spark plug well by the elastic means, in which 
     a) the material of the connector sleeve (3) has a high melting point and a high electric strength; 
     b) the gap between the connector sleeve (3) and the ceramic shaft of the spark plug is sealed by an elastic means (17) attached to the connector sleeve, by which means the spark plug connector is guided during plug-in onto the spark plug; 
     c) in the connector sleeve (3) a ceramic inlet (7) is provided which encloses the plug-in contact (28) and the ignition cable connection (32), with the plug-in contact (28) and the ignition cable connection (32) being embedded in the ceramic inlet (7) in such a way that the ceramic part in axial direction protrudes beyond the plug-in contact (28) and the connection (32) for the ignition cable.

The invention relates to a spark plug connector for an internalcombustion engine, comprising

a plug-in contact for the electrode connection of a spark plug;

a connector sleeve surrounding the plug-in contact;

a connection for an ignition cable;

a single-piece, rigid, supporting connector sleeve made of an insulatingmaterial; and

an elastic means attached to the connector sleeve which seals the gapbetween the connector sleeve and a spark plug well of an enginecylinder, with the spark plug connector being guided in the spark plugwell by the elastic means;

an elastic means attached to the connector sleeve which seals the gapbetween the connector sleeve and the ceramic shaft of the spark plug;

a ceramic inlet provided in the connector sleeve, which ceramic inletencloses the plug-in contact and the ignition cable connection, with theplug-in contact and the ignition cable connection being embedded in theceramic inlet in such a way that the ceramic part in axial directionprotrudes beyond the plug-in contact and the connection for the ignitioncable.

When many years ago gas was discovered as a fuel for industrial sparkignition engines, various engine manufacturers converted their dieselengines to gas engines, with the diesel injector nozzles being replacedby spark plugs. These spark plugs were located very deep in theso-called spark plug well, i.e. where previously the tip of the injectornozzle was installed in the cylinder head. A connection to the ignitioncoil was established by insulated or uninsulated metal extensions and anadditionally plugged-on ignition cable.

With the usual ignition voltages at this time, up to 15 kV maximum, theexisting gap in the spark plug wells provided sufficient insulation.

The emission ordinance TA-Luft ("Technical Instruction for thePrevention of Air Pollution") enacted in the meantime imposes lower NOxand CO levels. These lower levels could only be achieved by an engineoperating on a lean mixture. This meant that the engine designers had tocreate an excess of air in the combustion chamber. To achieve this,carburetion was optimised. This also included the development offour-valve cylinder heads. Increasing the number of valves resulted onthe one hand in a reduction in the diameter of the spark plug wells, andon the other hand in an increased voltage requirement at the electrodesbecause the lean mixture was more difficult to ignite. Ignition voltagewas increased to approximately 40 kV.

This leads to extremely unfavourable operating conditions including therequirement to conduct high voltages along extended distances in thenarrow spark plug well. Frequent arcing is still the order of the day,in particular if the electrode gap of the spark plug reaches a certaindimension. Most of the time such arcing occurs between the spark plug orspark plug extension and the spark plug well; arcing leads to misfiring.

In order to improve the operational behaviour, the use ofsilicon-sheathed spark plug connectors was proposed, with the said sparkplug connectors requiring insertion into the deep spark plug well bymeans of special pliers until they engaged the spark plug. Suchinstallation was extremely difficult and resulted in the ignition cablesbeing destroyed during de-installation. In addition, high maintenancecosts were incurred.

From DE 29 04 007 C2 the combination of a hollow-cylinder insulatingsleeve made of soft material is known, with a cylindrical retainer madeof a heat-resistant, hard insulating material such as Bakelite or hardrubber, to avoid radiated interference in the case of a spark plugconnector. However, the electric strength of such material combinationsis insufficient.

From DE 38 35 984 A1 a spark plug connector is known in which aninsulating elastomeric shoe comprises a rigid cover made of a thin, firminsulating material such as plastic. This combination only improvesremoval of the spark plug connector, without increasing the electricstrength.

From DE 33 02 878 A1 a spark plug connector is known which comprises asingle-piece, rigid, supporting and elastic insulation sleeve. Theinsulation sleeve comprises an insulating body made of thermosetmaterial or thermoplastic material, which insulation sleeve byspray-application directly envelopes a constructional unit comprising aninterference eliminating resistor, a connection component of theignition cable, and contact component for the spark plug. The insulationsleeve can be inserted into the spark plug well of an engine cylinder bymeans of a plug-on adapter with an annular sealing flange, with the saidconnector sleeve being elastically sealed against the said enginecylinder. In this way, the plugging-on of the spark plug connector isintended to be facilitated.

From EP 0 488216 A2 and U.S. Pat. No. 5,391,100 the use of a hardartificial resin with excellent heat resistance and electricalinsulation, as a material for the connector sleeve, is known.

DE-PS 839 285 discloses a spark plug connector with a ceramic insulatingbody enclosing a plug-in contact for the electrode connection of a sparkplug and a connection for an ignition cable.

DE-PS 29 48 043 and JP 4-12 486 A discloses the sealing, elasticguidance of the spark plug connector in the spark plug well of an enginecylinder or the connector sleeve on the ceramic shaft of the spark plug.

From EP 0 433 870 A1 a spark plug connector for motor vehicle engines isknown in which the ignition cable connection, a discharge tube and partof a connecting component to the spark plug are embedded in athermoplastic material, with additionally a protective tube made from aninorganic material such as ceramic or glass covering the said spark plugconnector. Such embedding which is intended to provide better protectionagainst corona discharge, does not meet higher requirements.

In addition, the use of ceramic-sheathed spark plug extensions wasproposed. However since there are only ceramic sleeves available on themarket which are intended as heat shields for thermal elements, theireconomical porous design cannot provide adequate resistance to highvoltage.

Due to the CE certification standard, gas engines must not exceedcertain interference-frequency limits. However, due to their unshieldedconducting of high voltages, the high tension cables used representgiant aerials.

It is the object of the invention to provide a spark plug connector forinternal combustion engines, comprising high heat resistance, increasedbreakdown safety and an extended serviceable life; which keeps away dirtand moisture from the spark plug well and from the insulator of a sparkplug, which suppresses radiated interference as far as possible andwhich is easy to install.

According to the invention, this object is met by combining thefollowing features:

a) the connector sleeve in the area of the ceramic inlet comprisesseveral shoulders in whose areas the ceramic inlet and the sleevematerial of the connector sleeve adjoin all around in a positive fit.

a) the material of the connector sleeve has a high melting point and ahigh electric strength, corresponding to those ofpolytetrafluoroethylene (PTFE).

If the connector sleeve in the receiving area of the ceramic inletcomprises several shoulders in whose areas the ceramic inlet and thesleeve material of the connector sleeve adjoin all around in a positivefit, then a further cause for possible breakdown is eliminated becauseany gaps between the ceramic inlet and the connector sleeve are avoidedor interrupted.

A further embodiment of the invention provides for the axial extremitiesof the ceramic inlet, in the contact areas where they touch theshoulders in axial direction, to adjoin in a positive fit, the connectorsleeve enclosing the ceramic inlet sleeve. In this case too, gaps andedges which may cause breakdowns are avoided.

In a further embodiment of the invention a radial restraint is added tothis axial restraint, in such a way that the surface of the sheath ofthe ceramic inlet along the length of the sheath, in a positive fit,radially touches by its shoulders the spaced apart contact areas of theconnector sleeve surrounding the sheath surface. This results in severalcontact surfaces, spaced apart, between the ceramic inlet and theconnector sleeve, by means of which misfiring is suppressed to a verysignificant degree.

A sleeve material comprising a rigid, insulating material with a highmelting point and high electric strength such as polytetrafluoroethylenecan easily be shaped and adapted to any desired forms of spark plugwells. A connector sleeve made of such material, which sleeve extendsthrough the gap to the spark plug well, significantly increases thebreakdown resistance if it is sealed from the spark plug well on the onehand and the spark plug on the other hand. The ceramic inlet itselfprovides further protection to the plug-in contact for the spark plugand the ignition cable connection, against arcing in longitudinal andlateral direction. This also increases breakdown resistance.

Up to now, the voltage to be provided by the ignition coil for the sparkto find its way to the mass, was determined by the engine parameters,such as temperature, pressure, mixture formation in the cylinder andelectrode gap of the spark plug. If the ignition voltage supplied by theignition coil to the electrode drops as a result of losses in theconnection, in particular in transition areas such as at the plug-incontact and at the ignition cable connection, then there is the dangerof electrode bridge formation which prevents the generation of anignition spark. Misfiring results. The spark plugs will need to bereplaced. As a result of the high electric strength and the optimalshielding of the ignition voltage against mass, achieved according tothe invention, it is now possible to provide a high ignition voltage ofapproximately 50-60 kV at the electrode thus ensuring safe ignition,because as a result of good shielding, no leakage currents and/or arcingoccur at other points. There are no electrode bridges, thussignificantly prolonging the serviceable life of the spark plug.Extension of the serviceable life is at a magnitude of 3 to 5 times thatof known ignition connections.

Apart from extending the serviceable life of spark plugs, the ignitionconnection comprising the ignition cable with the integrated plugconnector offers the additional advantage of avoiding consequentialdamage as a result of misfiring. Gas engines are fitted with catalyticconverters to reduce emissions. These catalytic converters are sensitiveto misfiring. If as a result of misfiring, non-combusted gas flowsthrough a catalytic converter, this can destroy the catalytic converter.If misfiring is avoided by means of the ignition connection according tothe invention, the catalytic converter is saved.

It is advantageous if within the ceramic inlet in the leads between theplug-in contact and the ignition cable connection an ohmic resistor isprovided, as is known from DE 33 02 878 A1. The resistor suppresseselectrical malfunctions. However it is equally important that this ohmicresistor reduces the spark duration and the spark decay time. By keepingthe spark duration and the subsequent spark decay time short, materialremoval from the spark plugs can be reduced, thus increasing theserviceable life of the spark plugs. It is advantageous if the value ofthe resistor is approximately 5 kOhm.

A further embodiment of the invention provides for all electricallyconducting components to be of extremely round shape. Since ignitionsparks always tend to spark over in pointed positions first, theinclination to arc over is reduced.

A further embodiment of the invention provides for the exterior of theconnector sleeve to comprise an O-ring which closes the gap between theexterior of the connector sleeve and the wall of the spark plug well,with ventilation slots extending in longitudinal direction of theconnector sleeve, between its outer sheathing and the O-ring. Thisprevents the formation of condensation in the gap, which can occur inspite of preventing access to dirt. In addition, overpressure can beevened out in spite of the gap being sealed. Oil, dirt and humiditywhich are among the major contaminants, are thus prevented from lodgingin the spark plug well. Sealing can also take place by means of anotherheat-resistant component, in particular a silicon material.

From DE 41 01 375 C1 it is known to keep away humidity from the gapbetween the connector sheathing and the ignition cable, by means of aroll ring.

It is also advantageous if in the area of the connector base at theinterior wall of the sleeve at least one O-ring is provided, with theexterior diameter of the said O-ring being such that it provides a tightseal against the ceramic collar of a spark plug. This seal which isknown from EP 0 248 717 protects the ceramic collar of a spark plug fromcontamination, thus preventing the occurrence of an increased transitionresistance between the plug-in contact and the spark plug. The seal alsoprevents leakage current moving down along the insulator which wouldcause misfiring in the engine compartment. Here again, instead of anO-ring, a silicon component, for example a silicon tube, might beconsidered for use.

A further embodiment of the invention provides for all components suchas connector sleeve, ceramic inlet, seals, plug-in contact, ignitioncable and similar, as far as is possible to comprise a silicon sheath.This results in an extremely high electrical breakdown resistance of allcomponents.

Below, the invention is further illustrated by means of a drawing, asfollows:

ceramic inlet and the connector sleeve, which gaps may cause instancesof breakdown, are avoided.

A further embodiment of the invention provides for the axial extremitiesof the ceramic inlet, in the contact areas where they touch theshoulders in axial direction, to adjoin in a positive fit, the connectorsleeve enclosing the ceramic inlet sleeve.

In a further embodiment of the invention a radial restraint is added tothis axial restraint, in such a way that the surface of the sheath ofthe ceramic inlet along the length of the sheath, in a positive fit,radially touches by its shoulders the spaced apart contact areas of theconnector sleeve surrounding the sheath surface. This results in severalcontact surfaces, spaced apart, between the ceramic inlet and theconnector sleeve, by means of which misfiring is suppressed to a verysignificant degree.

Below, the invention is further illustrated by means of a drawing, asfollows:

FIG. 1 shows a partial section of a spark plug connector for theignition connection of an internal combustion engine, to a spark plug;

FIG. 2 shows the spark plug connector with an ignition cable connected;

FIG. 3 shows a modified connector base of the spark plug connector withtwo O-ring seals.

The spark plug connector 1 according to FIG. 1 comprises a supportingconnector sleeve 3 made of a plastic material with a high melting pointand a high electric strength. Presently a suitable material for this ispolytetrafluoroethylene (PTFE). The material of the connector sleeve 3is approximately 5 mm thick. The connector sleeve 3 is of single-piecedesign comprising a central longitudinal bore 4 extending from theconnector base 5 to the connector head 6a. In the area of a ceramicinlet 7 in the direction of the connector base 5, the bore 4 is enlargedin steps, comprising shoulders 6, 8, 9. The first shoulder 6 forms anaxially internal end stop for the ceramic inlet 7. The diameter of theinternal wall 3a of the connector sleeve 3 is enlarged in steps in thearea of the ceramic inlet 7 at shoulders 8 and 9, in such a way that theexterior sheath surface 10 of the ceramic inlet 7, at shoulders 8 and 9adjoins around its entire circumferential area, all around with apositive fit and sealing along ring-shaped contact surfaces 11 and 12,against the material of the connector sleeve 3. Thus, spaced apart, theshoulders 8 and 9 repeatedly provide a safe positive fit, thus leadingto increased breakdown resistance.

With the ceramic inlet 7 in place, at the extremity near the connectorbase, this ceramic inlet 7 is secured by a recessed shoulder step 14 inwhose interior wall 15 the diameter of the bore 4 is reduced incomparison to the diameter of the wall area 16 in front of it. In thisway the ceramic inlet 7 is firmly seated in a positive fit in theconnector sleeve 3 between the shoulders 6 and 14, also in longitudinaldirection 25. In the area of the connector base 5, at the interior wall15, an O-ring 17 is provided whose external diameter is such that it canprovide a seal against the ceramic collar of a spark plug (not shown).In such a way the plug-in contact 28 is protected against contaminationwhich can cause an increase in the transition resistance at thisposition. In addition, the O-ring 17 provides an elastic guide at thespark plug for the connector sleeve 3. This is important because theengine vibrates during operation and unattenuated vibrations can damagethe plug-in contact 28. By means of O-ring 17, free vibrations betweenthe connector sleeve 3 and the spark plug are suppressed.

FIG. 3 shows a modified spark plug connector base 5. This connector base5 is longer than that according to FIG. 1, as far as this is compatiblewith the spark plug. For improved suppression of free vibrationmovements between the spark plug connector and the spark plug, in thiscase two O-rings 17 are provided, spaced apart.

In a middle region 18 the connector sleeve 3 comprises a snap-ringgroove 19 into which a further O-ring 20 is inserted. This O-ring 20ensures that the gap 22 between the external wall 23 of the connectorsleeve 3 and the spark plug well 24 is closed off so as to keep outcontamination such as oil, dust and the like. In longitudinal direction25 of the connector sleeve 3, in the area of the O-ring 20, longitudinalgrooves 26 are provided, to provide ventilation and pressureequalisation. Near connector head 6a there is a pull ring 27 whichenables improved gripping of the connector sleeve 3. This pull ring 27is intended for the mechanic, so as to prevent pulling by the ignitioncable 33 and thus pulling off the ignition cable 33.

While the connector sleeve 3 is made from PTFE which has a highbreakdown resistance and is easy to clean and easy to shape, the ceramicinlet 7 comprises a ceramic sleeve from a material which itself also hasa high breakdwon resistance. The plug-in contact 28 is inserted into theceramic inlet 7. Plug-in contact 28 and ignition cable connection 32 arerecessed in the ceramic inlet 7. Thus, in the direction of the connectorbase 5, the ceramic component protrudes beyond the plug-in contact 28,and in the direction of the connector head 6a it protrudes beyond theignition cable connection 32. The plug-in contact 28 changes into aconductive pin 29 which is connected to an ohmic resistor ofapproximately 5 kOhm. The resistor 30 reduces interference voltage andreduces the spark duration as well as spark decay time. The resistor 30in turn comprises a connection pin 31 ending in a connecting piece 32 towhich the ignition cable 33 is attached, for example by pressing it on.In this way the ignition cable 33 and the spark plug connector form aninstallation unit.

Of importance are the material combinations, with the interior being aceramic material and the exterior being PTFE, and thebreakdown-resistant connection between the two materials, and thesealing O-rings. This ensures high breakdown resistance. An additionalimprovement is achieved in that all metallic parts are rounded off toavoid spikes.

A further increase in the breakdown resistance can be achieved in thatboth the exterior sheath 10 of the ceramic inlet 7, the exterior sheath22 of the connector sleeve 3 and the ignition cable 33 comprise asilicon sheath 34, as indicated in FIG. 1.

FIG. 2 shows a top view of the ignition connection comprising the sparkplug connector 1, a plugged-on connector cap 34 and the ignition cable33. Also shown is the pull ring 27 by means of which the spark plugconnector 1 can be pulled from a spark plug well, and the O-ring 20which seals the spark plug well 24.

The ignition connection is preferably provided for operation with 50-60kV; it is characterised by a significantly improved breakdown resistanceand significantly improved serviceable life.

FIG. 3 shows a sectional view of an extension of the connector base 5 ofthe connector sleeve 3. With this embodiment, two O-rings 17, spacedapart, are provided. The second O-ring 17 improves vibration security inthose instances where the collar of the spark plug is sufficiently long.

What is claimed is:
 1. A spark plug connector for connecting to aceramic shaft spark plug for use in a spark plug well of an enginecylinder in an internal combustion engine, comprising:a plug-in contactfor the electrode connection of a spark plug; a single-piece, rigid,supporting connector sleeve surrounding the plug-in contact and made ofan insulating material; a connection for an ignition cable; a firstelastic means attached to the connector sleeve which seals a gap betweenthe connector sleeve and the spark plug well, with the spark plugconnector being guided in the spark plug well by the elastic means, asecond elastic means attached to the connector sleeve which seals a gapbetween the connector sleeve and the ceramic shaft of the spark plug; aceramic inlet provided in the connector sleeve which encloses theplug-in contact and the ignition cable connection, whereby the plug-incontact and the ignition cable connection are embedded in the ceramicinlet such that the ceramic inlet axially protrudes beyond the plug-incontact and the ignition cable connection, further characterized by:a)the connector sleeve in the area enclosing the ceramic inlet comprisesshoulders for providing a positive fit between the ceramic inlet and thesleeve material of the connector sleeve; and b) the material of theconnector sleeve has a high melting point and a high electric strength.2. A spark plug connector according to claim 1, characterized in thatthe ceramic inlet comprises axial extremities for touching the shouldersfor axial fixation, in axial direction to adjoin the ceramic inlet in apositive fit in the portion of the connector sleeve enclosing theceramic inlet.
 3. A spark plug connector according to claim 1 or 2,characterized in that ceramic inlet comprises a sheath for radiallytouching the shoulders for radial fixation along the length of thesheath to provide a positive fit with the portion of the connectorsleeve surrounding the sheath surface.
 4. A spark plug connectoraccording to one or several of claims 1 to 3, characterised in that allelectrically conducting components are of extremely round shape.
 5. Aspark plug connector according to claim 1, wherein the first elasticmeans comprises an O-ring and wherein the connector sleeve is furtherprovided with ventilation slots extending in longitudinal direction ofthe connector sleeve, between the outer sheathing of the connectorsleeve and the O-ring.
 6. A spark plug connector according to claim 5,wherein the connector sleeve, ceramic inlet, first elastic means, secondelastic means, plug-in contact, and ignition cable comprise a siliconesheath.
 7. A spark plug connector according to claim 1 wherein theconnector sleeve in the area enclosing the ceramic inlet comprises fourshoulders for providing a positive fit between the ceramic inlet and thesleeve material of the connector sleeve.